The present invention relates generally to apparatus for generating a gas-borne powder stream and, more particularly, to apparatus for the application of a powder to a work piece. The invention finds particular utility in the fabrication of threaded devices having a coating of fusible thermoplastic resin.
It is now conventional in the threaded fastener industry to apply various coatings to the threads of fasteners to achieve predetermined performance characteristics. The coating may provide enhanced frictional engagement, or a self-locking function. It may create an adhesive bond between the fastener and a mating threaded device. Other coatings are also used for lubrication, masking and electrical insulation. Often, such coatings are formed by applying a stream of air-borne thermoplastic resin particles onto the fastener which has been preheated to a temperature above the resin's melting point. Upon impact, the resin particles melt and fuse into a coating which will adhere to the fastener when the resin cools and resolidifies.
Examples of prior art apparatus used in the fabrication of such coated threaded devices are disclosed in U.S. Pat. Nos. 4,120,993; 4,775,555; 4,815,414; 4,842,890; 5,090,355; 5,141,375 and 5,221,170.